linksys oddities with directional antenna

- J
- jamessmalljr
  
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posted
18 years ago

Tue, Apr 18, 2006 1:38 PM

I have a linksys WRT54GS using DD-WRT firmware with a high gain directional antenna to another access point some distance away (800-1000 feet).

When I plug ethernet into the WRT54GS, I can communicate without issue.

When I attempt to use a wireless connection into the WRT54GS, it 'sorta works sometimes', it's as if the box is deciding that there's a better signal here, and it broadcasts/receives over the stock omni antenna, instead of other the high gain antenna to talk to the other access point.

Any suggestions? I'm thinking I may just have to buy an additional access point, and ethernet connect it to the roof mounted (high gain antenna), and force the roof mounted one to only use the high gain antenna, and to ignore the stock omni.

- D
- Derek Broughton
  
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posted
18 years ago

Tue, Apr 18, 2006 2:20 PM

I was told here that that was exactly the behaviour to expect, so I was surprised after installing Talisman to find that it works fine for me. How is your local WRT54 configured? Mine is in WDS mode, which I'm pretty sure you need to do this.

- J
- Jeff Liebermann
  
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posted
18 years ago

Tue, Apr 18, 2006 4:24 PM

snipped-for-privacy@gmail.com hath wroth:

That's exactly what's happening. The diversity reception is not designed to play load balancer between your distant link and your local wireless laptops. The algorithm involved is that the antenna that received that last valid packet is selected. The access point will continue using that antenna until it gets a high packet error rate, at which time it will try the other antenna. That works quite well for reducing the effects of momentary reflections but is useless for doing a balancing act between two radically different wireless clients.

I once read a much better explanation somewhere on the web but can't find it right now.

The algorithm seems to be (I'm not sure) etched in silicon and vary with chipset vendor. Some chipsets are more aggressive on switching antennas, while others stay glued to their favorite antenna. I don't know which end the Broadcom chipset in the WRT54G fits. My guess is toward the tenacious end because every time I've tried a similar arrangement, I have a similar problem.

Yep, that's the right way to do it and should work just fine. However, there are some ugly alternatives:

If you have 3 dB surplus gain or tx power in your outdoor wireless link, you can attach a power splitter to the antenna. Disable diversity and select just one antenna. Each antenna (indoor or outdoor) gets half the tx power. Be prepared to deal with a mess of cables and connectors.
formatting link
A variation of the above is to "leak" some RF near the WRT54G using do-it-thyself leaky coax (Radiax). I made a custom pigtail out of about a 1 meter piece of LMR-240, where I had gouged out 1/4 wave electrical slots in the shield with a Dremel tool and knife. It leaked just enough RF to allow using a laptop in the room where the WRT54G was located.